1. Field of the Invention
The present invention is directed to a pulse tube refrigerator and in particular to a pulse tube refrigerator for cooling a specific device below a temperature, which can be connected thereto in easier manner and with improved refrigerating efficiency.
2. Discussion of the Background
A conventional pulse tube refrigerator is disclosed in U.S. Pat. No. 5,515,685. Similar pulse regenerators are also disclosed in U.S. Pat. No. 5,522,223 and U.S. Pat. No. 5,335,505.
The conventional pulse tube refrigerator includes a pulse tube and a regenerator arranged in parallel thereto in such a manner that lower temperature ends of the pulse tube and the regenerator are in fluid communication with each other. The lower temperature ends of the pulse tube and the regenerator are mounted with a common cold head. The cold head is brought into contact with a member for cooling the same to a determined temperature in such a manner that coldness or an ultra low temperature generated at the lower temperature end of the pulse tube is transferred via the cold head to the member.
In the foregoing structure, a high or higher temperature end and a lower temperature end of each of the pulse tube and the regenerator, both of which extend in the downward direction, take higher and lower position, respectively. This means that the contact of the cold head with the member is established from the top thereof.
On the other hand, it is required to contact the cold head of the pulse tube refrigerator with the member to be cooled down from the bottom or a horizontal side thereof. In order to comply with such a need, it has been considered to establish such a connection after inverting the device or tipping the device down.
However, such an idea is not acceptable from a practical viewpoint. In detail, inverting the pulse tube refrigerator produces a higher position of the lower temperature end of the pulse tube and a lower position of the higher temperature end of the pulse tube, resulting in an occurrence of free convection of the working gas in the pulse tube. This free convection causes a movement of a higher temperature fluid at the higher temperature end to the lower temperature end and therefore such a heat movement acts as a heat load on the cold head. Thus, the resultant heat load on the cold head drops the refrigerating efficiency of the pulse tube refrigerator. Tipping the pulse tube refrigerator down makes a horizontal extension of the pulse tube. In the resultant condition, a temperature distribution of the working gas is disturbed in the pulse tube which disturbs a designed speed of the working gas in the pulse tube, resulting in that the refrigerating efficiency of the pulse tube refrigerator drops inevitably.